1. Field of Invention
The invention relates to the construction of an ink-jet head and a method of fabricating same.
2. Description of Related Art
An on-demand type ink-jet printer head using piezoelectric elements is disclosed in Japanese Patent Application Publication No. 8-276586. In the disclosed ink-jet head, a head unit is bonded, using an adhesive, to a head case made of a synthetic resin.
The head case is molded by injection of a synthetic resin. However, due to a fabricating error, an adhesive interposed between the head case and the head unit may be squeezed out. If the squeezed adhesive makes contact with ink to be supplied to the head unit, chemical reaction occurs. As a result, adhesive particles are dispersed into the ink and cause an ink ejection failure and ultimately clogging of the nozzle.
If the ink permeates into the adhesive, the ink may leak to the outside with the aid of air bubbles contained in the adhesive.
Another problem is that an ink-jet head is hard to fabricate with a high degree of accuracy by bonding using an adhesive. Especially, when a plurality of head units are bonded to a single head case, the mounting accuracy should be improved between the head units and the head case as well as between the head units. If such mounting accuracy is low, the direction and angle of the ink ejected from the nozzle becomes unstable, resulting in poor printing quality.
The invention addresses the forgoing problems.
In an ink-jet head according to the invention, a head unit is bonded to a frame such that an ink supply hole provided in the head unit faces an aperture of an ink supply passage formed in the frame. A groove is formed around the rim of the aperture. A packing is fitted into the groove and a sealant is filled around the packing. The packing and the sealant cooperate to seal a gap between the aperture and the supply hole.
When an ink-jet head is fabricated, the packing is brought into contact, at its end, with the backside of the head unit so as to surround the supply hole. While a gap between the aperture and the supply hole is sealed, a sealant is filled into the outer rim of the packing. The filled sealant does not enter, beyond the packing, the inner rim thereof. Accordingly, the effective area of the ink supply hole is not reduced. In addition, because ink does not contact the sealant, no chemical reaction occurs therebetween and the performance of the ink-jet head can be maintained.
By pressing the head unit and the frame relative to each other, the backing sinks into the groove while the end of the packing is kept in intimate contact with the backside of the head unit so as to surround the ink supply hole and while the inner rim face of the packing is kept in intimate contact with the inner rim wall of the groove. Such intimate contact between the end of the packing and the backside of the head unit does not permit the sealant, if it overflows the packing, to enter the inside diameter portion of the packing.
Accordingly, the sealant makes intimate contact with the head unit in the outer rim of the packing and tightly seals the supply hole.
Preferably, the head unit and the frame are bonded to each other using a quickly hardened adhesive, such as an UV adhesive to be hardened under ultraviolet irradiation. Use of a quickly hardened adhesive eliminates the need for pressing the head unit and the frame for a long time and prevents them from being deformed. In addition, the accuracy of mounting the head unit can be improved by reducing its positioning error and, as a result, print quality can be improved. Use of a quickly hardened adhesive, which is hardened in a very short time, will substantially improve efficiency of an assembling process.
Further, by simultaneously irradiating a plurality of UV adhesive-applied portions with ultraviolet light, the adhesive in the plurality of portions can be simultaneously hardened. This prevents the head unit and the frame from being distorted.
Especially, by applying the adhesive near the four corners of one head unit, a displacement of the head unit caused by contractionary distortion of the adhesive, when it is hardened, can be minimized.
Further, bonding the head unit, at its four corners, to the frame prevents the head unit from being deformed when a rubber cap is pressed against a nozzle face to perform a nozzle restoration operation.
Further, the accuracy of mounting the head unit can be improved by providing positioning holes in a nozzle plate and by fitting the nozzle plate into a jig having positioning pins corresponding to the positioning holes. Especially, when a plurality of head units are mounted side by side on the frame, not only the mounting accuracy between the head unit and the frame but also the mounting accuracy between the head units can be improved.